RFD: Add Linux/AArch64 to the set of supported OpenJDK platforms

[Andrew Haley]

https://bugs.openjdk.java.net/browse/JDK-8044552
http://openjdk.java.net/jeps/8044552

The AArch64 port has been complete for some time, and the rate of
churn has slowed to the point where I believe it is stable enough to
be moved into the mainline sources.  It has passed the full JCK on JDK
7 and 8, but as yet there is no JCK 9, so I can say nothing about
that.  We are regularly testing using jtreg, Hadoop, and a bunch of
other tests, and our results are similar to the same tests on x86.

I hope that this process will be less involved and require less effort
from approvers (at Oracle and elsewhere) than that for the Power PC
port.  I believe this because there are few changes to shared code
beyond the trivial #ifdefs for header files which appear in many
places.  In a few places we've had to #ifdef out code which is in
src/share but makes architectural assumptions which are not valid on
AArch64.

So, our proposal as detailed in the JEP is to create a staging forest
which at the start will be a clone of the current JDK9.  This staging
forest will have jcheck fully enabled (unlike the AArch64 development
repositories).  We will then submit webrevs for approval to the
appropriate groups, and then check them in to the staging forest.

I presume that for each webrev it will be necessary to create a Jira
Issue.

A few questions arise:

To which mailing lists should requests for approval be sent?  I'm
guessing hotspot-dev for the HotSpot patches, and jdk9-dev for
everything else.

What should the granularity of the webrevs be?  I don't think that any
subset of the src/cpu/aarch64 directory would make sense, but it's a
big bite to chew.

The JEP, which was based on that for the Power PC, talks about a more
detailed Integration Plan in the AArch64 Port OpenJDK Wiki Space, but I
have no plans beyond submitting webrevs for approval.

Is there anything else we should do before creating issues and
submitting webrevs?

Thanks,
Andrew.